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Subtle chemical differences among individual cells and cells within tissue sections can be detected by imaging mass spectrometry analysis of the cellular contents. We are using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) to image and identify individual cells based on their characteristic mass spectra. A surface scanning procedure, ToF-SIMS is uniquely suited to the sensitive detection of a spectrum of masses that provides a rich sample of the molecules and fragments that together comprise a chemical map of the cell. ToF-SIMS measurements involve utilizing a finely focused primary ion beam to desorb secondary molecular ions into a time-of-flight mass spectrometer. The mass spectra generated can be used to produce high-resolution chemical images of individual cells or tissue sections that can be further compared with standard hematoxylin & eosin stained images. Using the large spectral data sets generated by ToF-SIMS analysis in conjunction with pattern recognition statistical analysis, we have differentiated breast cancer cells that differ in cancer phenotype. We are also using this technique to correlate specific chemical signatures to organ types. In a preliminary experiment, sixteen-day old mouse embryos were paraffin embedded, sectioned and analyzed using ToF-SIMS. Seven tissue types were selected for imaging and the resulting spectra were analyzed by PCA. Despite the paraffin embedding, the seven tissue types were well separated on the resulting PCA score plot. We have also analyzed prostate tissues from a tissue microarray to determine differences among normal and cancerous tissues. We found that normal stroma was distinct from normal epithelial cells within the same biopsy section. Within the tissue array, samples identified by standard pathology as cancerous were compared to non-cancerous. PCA of ToF-SIMS spectra from these regions showed grouping of similar tissue types and separation of cancerous from non-cancerous cells. These studies illustrate the power of ToF-SIMS to detect and identify single aberrant cells within a normal cell population or tissue sample. The mass signatures generated by ToF-SIMS analysis have the potential to contribute to a better understanding of the carcinogenic process including identifying stages of tumorigenesis and metastasis of the primary tumor to other organs. (This work was performed under the auspices of the U.S. DOE by LLNL under contract no. W-7405-Eng-48 and supported by NCI: CA55861, EDRN: CA086-366, CBCRP: 10IB-0077 and LDRD: 04-ERD-104).

[Proc Amer Assoc Cancer Res, Volume 47, 2006]